Process for producing magnesium ore briquettes



J. P. DICK F ch. 3, 1948.

PROCESS FOR PRODUCING MAGNESIUM ORE BRIQUETTES Filed June 21, 1944 m N T Patented Feb. 3, 1948 PROCESS FOR PRODUCING MAGNESIUM ORE BRIQUETTES John Parsons Dick, Haley, Ontario, Canada, assignor to Dominion Magnesium Limited, Toronto, Ontario, Canada, a corporation of Ontario, Canada Application June 21, 1944, Serial No. 541,428

. In Canada May 11, 1944 4 Claims. (01. 75-67) This invention relates to the production of metallic magnesium by thermal reduction of magnesia containing material, and is particularly concerned with the treatment of calcined dolomite and the like in the briquetting of the material with a reducing agent, such as ferrosilicon.

The invention is particularly useful in the treatment of calcined dolomite and the like for the production of briquettes to be used in the procedure disclosed in United States Patents 2,330,142 and 2,330,143 but may be employed elsewhere in the production of dense briquettes.

Much difiiculty has been experienced in producing satisfactory briquettes from the calcined magnesia containing'material. Briquettes which are not sufiiciently dense and strong permit the formation of much fine material before they are charged into a thermal reduction chamber, which prevents the efficient transfer of heat through the charge. Removal of such fine material before it is charged, is an expensive procedure, and necessitates recirculation of the fine material back to the briquetting circuit and requires extra briquetting capacity to handle same. Various methods have been proposed and tried for rendering the calcined material more dense and the briquettes more durable.

It has now been found that greatly improved results accrue from the provision of a closely controlled and uniform moisture content in the calcined material to be briquetted.

The primary object of the present invention is to provide a method of treating the calcined material whereby a desired moisture content may be provided therein, so that more dense and durable briquettes may be produced therefrom.

Other objects of the invention will appear from the following description taken in conjunction with the accompanying drawing which shows a form of apparatus for carrying out the invention and in which Figure 1 is a diagrammatic longitudinal elevation of the apparatus,

Figure 2 is a broken longitudinal elevation, partially in section, of a rotary cooling device in which the moisture content of the calcine is controlled, and

Figure 3 is an end elevation of the cooling device.

In the drawing l is a rotary calcining kiln connected to a stack 2 which is provided with a draft control vent 3. The rock is fed to the kiln by the pipe 5 and 6 is a fuel burner. i is a rotary cooling device which receives the calcine from the kiln through the chute 8 within the hood 9 which encloses the discharge end of the kiln and the charging end of the cooler. The kiln and cooler are mounted for rotation in any desired known manner. A pipe I0 is centrally located along the longitudinal axis of the cooler I and preferably terminates a short distance from the charging end of the cooler, where spirally arranged vanes H are secured to the drum to feed the calcine into the space i2 between the pipe and the wall of the drum. In this space are located angle irons I3 to lift and agitate the calcine as the drum rotates. At its discharge end a section of the cooler drum is in the form of a screen l4 through which the fine materials pass to a conveyor [5 or the like, while oversize particles are discharged at the end of the drum and removed by any suitable means It. A pipe I! is arranged at the dicharge end of the cooler for the delivery thereto of steam or water vapour. It may have two branches ill for uniform distribution of the steam.

An adjustable closure is provided for the discharge end of the cooler to regulate the amount of air admitted to the space I2 and preferably without interfering with the amount of air entering the pipe l0. As shown this closure comprises two arcuate members l9 and 20 slidably mounted on vertical standards 2|. A lever 22 pivoted on cross bars 23 fixed to the standards and connected to the arcuate members by links 24 controls the vertical movement of the members. The arcuate members have fiange portions 25 and 28 extending rearwardly over the screened section of the drum to prevent undue entry of air through the screen. Flange portion 28 is cut away at 27 to permit discharge of fine material through the screen and the arcuate member 23 has a forwardly spaced portion or bulge 28 to permit discharge of oversize material.

In operation the natural humidity of the atmosphere must be taken into consideration and adjustments must be made in accordance there with. Efiicient operation of the calcining kiln requires the passage through the kiln to the stack of an adequate amount of air. This air is admitted through the cooler l, in which it cools the calcine, and passes in its preheated condition to the kiln I. In the cooler the hot calcine naturally absorbs moisture from the air and the amount of moisture absorbed varies with the humidity of the air. Accordingly the invention provides for the control of the amount of moisture actually taken up by the calcine.

In the production of dense, durable briquettes it has been found that the moisture content of the calcine to be briquetted should be within the 1 range of 0.6 to 0.8%, when the briquettes are to be used in the production of magnesium as previously indicated. When the briquettes are used for furthertreatment where the loss onignition is not of so muchooncern the upper limit of the moisture content is not so critical. Briquettes having this moisture content are hard and have I a density of from 1.9 to 2.2. The addition of steam to provide the specified moisture content Fewer fines are thus formed in' handling the'b'riquettes. In one installation the amount of fines to be returned to the presses for rebriquettingwas reduced by about 25 The moisture content of the calcine is con-. trolled by admitting steam to the cooler,'by the" pipe [7, to insure a substantially constant humidity level in theair'within the cooler and which contacts the'calcin'e 'as the latter is agitated by the rotation of the cooler. In. wet,

weather the natural humidity of the air may provide enough moisture to raise the moisture content of the calcine to the desired level but such'conditions vary greatly from',day today and with the seasons. Thus theadjustableclo-i tially increases the eifective capacity of the briquetting processes, an increaseof 16.7 having been obtained. The power consumption-of the presses is more constant and there is, less danger of breaking the'briquetting roll shells. More-finely divided material may bebriquetted,

satisfactorily. For example, it has-been found that'the proportion'of -20,0-mesh calcined material may be increased from 30% to 65% and still produce improved-briquettes.

In recovering magnesium from calcined-dolomite briquettes as described, the magnesium production was increased by 4 or 5%and required .10 in the calcine has the effect of increasingthe density of the briquettes by substantially 8% I and at the same time they are much harder.

less ferrosilicon to reduce the magnesia. Furthermore, the reduction in fines appearing in the retorts results in a decrease in the tendency for the residue to fuse and form scale on the wall of the retorts. i I

While the --method of briquetting 'has been particularly described with reference to the production of magnesium this invention is intended to be restricted only by the appended claims. It will be apparent that various changes may be made without departing from the spirit or scope of the invention as defined.

'I claim: 1

1. In the"production of briquettes from finely divided"materialconsisting essentially of magnesia, the improvement of which comprises inco porating substantially 0.6 to 0.8% by weight of moisture in the material and pressing the ma terial into briquette form.

2. A method as defined in claim 1 in which the material hot pursuant tocalcination is cooled in a humid atmosphere from which it absorbs moisture.

,3. A method as defined'inclaim 1 in which the material hot pursuant to calcination is cooledin the presence of airan'd water vapour is admitted to the air to be'absorbed by the material.

4. A-method as defined in. claim 1 in which the material hot pursuant to calcination is cooled in acounter-cur'rent of moistair and the counterecurrent flow'lof air is co'ntrolled to fre'gulate theamount of moisture absorbed by the material.

JOHN PARSONS DICK.

REFER/ENCES CITED file of this patent:

UNITED STATES PAIENTS Number Name Date r 2,219,427 Morris Oct.'29, 1940 2,295,105 Gloss et. al. Sept. 8, 1942 2,117,415 Goss. '-May 17, 1938 2,065,618 :Sherwood 'Dec. 29,1936 2,160,956 Cheesman June'6, 1939 2,323,597 Hansgirg July-6, 1943 2,393,080 Waring Jan. 15,1946 1,087,183 Ronay Feb. 17, 1914' FOREIGN PATENTS Number Country Date GreatBritainnnui Jan. '28, 1934 

